Video input to a typical display system is usually in the form of stimuli containing three driving signals, such as luminance-bandwidth-chrominance (YUV), luminance-chroma (blue)-chroma (red) (YCbCr), analog version of YCbCr (YPbPr), red-green-blue (RGB), and so forth. The stimuli with three driving signals can be expressed as three-dimensional color vectors. However, many display systems are multiprimary and use stimuli with, in general, N driving signals, where N is greater than or equal to three. Therefore, there is a need to convert the stimuli with three driving signals (the video input) into the stimuli with N driving signals used by the multiprimary display system.
With reference now to FIG. 1, there is shown a diagram illustrating a typical data flow 100 in a prior art technique for use in the conversion of stimuli with three driving signals (commonly presented as three-dimensional color vectors) into stimuli with N driving signals (N-dimensional color vectors) for use in a multiprimary display system. The prior art technique receives as input, the stimuli in the form of three-dimensional color vectors (denoted t), which can be converted into an intermediate color vector via a gamut mapping operation (block 105). The intermediate color vectors are in an intermediate common connection color space and must then be converted into the desired N-dimensional color vectors (denoted p) (block 110). The conversion can be expressed as a multiplication of the desired N-dimensional color vector, p, with a color matrix (denoted A) with dimension 3×N, which contains tristimulus values of the display system. The relationship between t, A, and p can be expressed as t=A*p or p=A−1*t. The desired N-dimensional color vector can then be used by the multiprimary display system.
With reference now to FIG. 2, there is shown an x-y chromaticity chart 200. The x-y chromaticity chart 200 illustrates a two-dimensional map of visible colors (shown as curve 205). In addition, the x-y chromaticity chart 200 illustrates displayable colors for an exemplary five-primary display system (shown as pentagram 210) with primary colors blue, yellow, cyan, red, and green, for example, as well displayable colors for an exemplary three-primary display system (shown as triangle 215) with primary colors red, green, and blue, for example. Consider a point inside the triangle 215 (shown as point C) that can be expressed as a combination of three weights (one for each color), such as C=WR*CR+WG*CG+WB*CB, where CR, CG, and CB denote chromaticity points of red, green, and blue, respectively, and WR, WG, and WB denote the amount of each color needed to generate the point C. Points inside the pentagram 210 can similarly be expressed as a combination of five colors. In general, points in the triangle 215 or the pentagram 210 can be generated by a large number of combinations of weights. An exception can be points that are in the pentagram 210 that are relatively close to the edge of the pentagram 210, such as point B, for example. Point B is close to a vertex of the pentagram 210 that represents pure cyan. The number of combinations that can generate the point B can be fewer than many other points within the pentagram 210 since the cyan primary has to be used in order to guarantee that the point B is placed at the proper point. This restriction reduces the number of possible combinations for the point.
For example, a pure yellow color can be generated as a combination of primaries (B=0, Y=0, C=0, R=255, G=255), or (B=0, Y=255, C=0, R=0, G=0), or (B=0, Y=255, C=0, R=255, G=0), or (B=0, Y=255, C=0, R=0, G=255), among others. Although many combinations can generate the same color, some combinations will be better than others. For example, some combinations may produce a brighter color than others. In a display system, increased brightness may be desired since image quality can be dependent upon image brightness. Additionally, some combinations may produce better results depending upon the chromatic characteristics of the display system. For example, combinations that minimize a transition of energy between primaries can produce images with a lower level of color noise.
One disadvantage of the prior art is that the prior art techniques compute an N-dimensional color vector that produces a color corresponding to a three-dimensional color vector without considering additional requirements on the selecting of the N-dimensional color vector that are realizable. Some of the N-dimensional color vectors, p, can have negative entries and more importantly, other N-dimensional vectors may improve image quality, such as minimize or eliminate color noise or reduce reproduction errors.